CN114083155A

CN114083155A - Method for laser cutting silicon wafer

Info

Publication number: CN114083155A
Application number: CN202111668297.5A
Authority: CN
Inventors: 蒋仕彬
Original assignee: Hangzhou Yinhu Laser Technology Co ltd
Current assignee: Hangzhou Yinhu Laser Technology Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-02-25

Abstract

The invention discloses a method for cutting a silicon wafer by laser, which is characterized by comprising the following steps: (1) providing a fiber laser with the wavelength of 2.0 +/-0.2 microns, wherein the fiber laser outputs a pulse laser beam with the pulse width not more than 100 nanoseconds; (2) focusing a pulse laser beam to the bottom surface through a silicon wafer to be cut, and moving a focusing point from bottom to top to form a longitudinal crack; (3) moving the focus point to the next position of the cutting track; (4) repeating the step (2) and the step (3) until a cutting envelope is formed; (5) and (5) splitting, and finishing cutting the silicon wafer. The invention reduces the heat affected zone and is particularly suitable for cutting silicon wafers used for photovoltaic cells.

Description

Method for laser cutting silicon wafer

Technical Field

The invention relates to a photovoltaic cell material, in particular to a method for cutting a silicon wafer for a photovoltaic cell.

Background

In the solar energy industry, the production of photovoltaic cells involves the cutting of large-scale silicon wafers, and at present, the wire cutting mode is still largely used, but the application of laser cutting is more and more.

Compared with the traditional mechanical cutting silicon wafer, the laser cutting has great advantages, such as: the cutting precision is high, the cutting seam is narrow, the quality is high, the yield is high, the waste of materials is avoided, and the cutting surface is smooth; as a non-contact cutting mode, the cutting tool does not deform or stain a product, and is a green and environment-friendly processing means; the most important point is that the cutting efficiency is greatly improved compared with the traditional cutting.

However, the existence of the heat affected zone of the laser cutting has a great influence on the photoelectric conversion efficiency of the photovoltaic cell, and although efforts are made to narrow the width of the heat affected zone generated in the cutting at present, which is about 150um, it is very difficult to achieve a lower heat affected zone.

The Chinese invention patent CN110085702B discloses a high-efficiency photovoltaic cell manufacturing method for effectively reducing laser cutting loss, wherein laser is used for scribing at a cutting mark position, then the scribed line is etched into a shallow groove through texturing or etching, and subsequent laser cutting is carried out along the shallow groove, so that the problems of cell efficiency reduction and cell damage caused by conventional cell cutting can be reduced by adding a new laser scribing step on the premise of not adding new production line equipment, wherein the wavelength of the first laser scribed at the cutting mark position is 200-800 nm. The scheme can reduce the influence of a heat affected zone on the photovoltaic cell, but a scribing process and a shallow groove etching process are required to be added in the processing process, so that the whole processing process is complicated, and the process time is prolonged.

Therefore, how to reduce the heat affected zone of laser cutting without complicating the process is of great significance for the application of laser cutting to silicon wafers for photovoltaic cells.

Disclosure of Invention

The invention aims to provide a method for cutting a silicon wafer by laser, which reduces the range of a heat affected zone so as to be suitable for cutting the silicon wafer for a photovoltaic cell.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: a method of laser cutting a silicon wafer, comprising the steps of:

(1) providing a fiber laser with the wavelength of 2.0 +/-0.2 microns, wherein the fiber laser outputs a pulse laser beam with the pulse width not more than 100 nanoseconds;

(2) focusing a pulse laser beam to the bottom surface through a silicon wafer to be cut, and moving a focusing point from bottom to top to form a longitudinal crack;

(3) moving the focus point to the next position of the cutting track;

(4) repeating the step (2) and the step (3) until a cutting envelope is formed;

(5) and (5) splitting, and finishing cutting the silicon wafer.

In the above technical solution, the pulse output may be a pulse that is uniformly distributed over time, and may be a pulse train, each pulse train includes at least two laser pulses, the time between each laser pulse in each pulse train is less than 90 nanoseconds, and different pulses in the same pulse train may have different pulse widths.

In the technical scheme, the optical fiber laser mainly comprises a seed laser and an optical fiber amplifier, wherein a laser beam output by the seed laser adopts the optical fiber amplifier to amplify energy and then outputs laser, and the peak power of each pulse of the laser beam is more than 10 kilowatts.

In the above technical scheme, the seed laser is a Q-switched fiber laser.

Or, the seed laser is a gain-modulated semiconductor fiber coupled laser.

In the preferable technical scheme, the output pulse width of the fiber laser is 1 ps-300 ps.

Or the output pulse width of the fiber laser is 0.5 ns-100 ns.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

in the prior art, the laser wavelength for cutting silicon wafers is usually between 193nm and 1064nm, and since the wavelength of a YAG laser (1064 nm) is considered to be well used for silicon with an electronic band gap, a 1064nm YAG laser is generally used in current commercial silicon wafer laser cutting equipment. However, since this wavelength is not transparent to the silicon wafer (absorption rate is 60% or more), the bottom-up dicing method cannot be used, but only from the top down. The invention uses 2 micron laser which is not used in the prior art, can penetrate through the silicon wafer, and can cut by adopting a bottom-up method, thereby reducing the heat affected zone, and being particularly suitable for cutting the silicon wafer used for the photovoltaic cell.

Drawings

FIG. 1 is a schematic flow chart of a method of an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of an apparatus according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of an apparatus used in the second embodiment of the present invention.

Wherein: 1. a cutting head; 2. a silicon wafer to be cut; 3. an X/Y axis horizontal movement mechanism; 4. a galvanometer; 5. an X-axis motion mechanism; 6. y-axis motion mechanism.

Detailed Description

The invention is further described with reference to the following figures and examples:

the first embodiment is as follows: referring to fig. 1, a method of laser cutting a silicon wafer includes the steps of:

(1) providing a fiber laser with the wavelength of 2.0 +/-0.2 microns;

the optical fiber laser mainly comprises a seed laser and an optical fiber amplifier, wherein a laser beam output by the seed laser adopts the optical fiber amplifier to amplify energy and then outputs laser, and the peak power of each pulse of the laser beam is more than 10 kilowatts.

The pulse output may be a pulse distributed uniformly in time, and may be a pulse train, each pulse train includes at least two laser pulses, the pulse width is less than 100ns and greater than 0.5ns, the time between each laser pulse in each pulse train is less than 90 ns, and different pulses in the same pulse train may have different pulse widths.

(3) moving the focus point to the next position of the cutting track;

(4) repeating the step (2) and the step (3) until a cutting envelope is formed;

(5) and (5) splitting, and finishing cutting the silicon wafer.

To carry out the above method, reference is made to the apparatus of FIG. 2. In the figure, a focusing light path is arranged in a cutting head 1, a laser beam is guided into the cutting head 1 and then is focused on a silicon wafer 2 to be cut, and the cutting head 1 can move up and down along a Z axis. The silicon wafer 2 to be cut is placed on a table having an X/Y axis horizontal movement mechanism 3. The cutting head 1 moves up and down to change the height position of the focusing point relative to the silicon wafer, and the X-axis and Y-axis horizontal movement mechanisms 3 drive the silicon wafer to change the relative position of the silicon wafer and the cutting head 1, so that the cutting envelope is realized.

Tests have shown that the width of the heat affected zone can be reduced to 80 microns by cutting in a bottom-up manner using the apparatus of this embodiment.

Example two: referring to fig. 3, there is another apparatus for carrying out the method of the present invention. A galvanometer 4 is arranged in the optical head, an optical system is arranged on an X-axis moving mechanism 5, and a silicon wafer to be cut is positioned on a workbench with a Y-axis moving mechanism 6. The movement of a focus point is realized through the matching of the galvanometer 4, the X-axis motion mechanism 5 and the Y-axis motion mechanism 6, and a cutting envelope is formed.

Tests have shown that the width of the heat affected zone can be reduced to 75 microns by cutting in a bottom-up manner using the apparatus of this embodiment.

Claims

1. A method for laser dicing a silicon wafer, characterized by comprising the steps of:

(3) moving the focus point to the next position of the cutting track;

(4) repeating the step (2) and the step (3) until a cutting envelope is formed;

(5) and (5) splitting, and finishing cutting the silicon wafer.

2. The method for laser cutting a silicon wafer according to claim 1, characterized in that: the optical fiber laser mainly comprises a seed laser and an optical fiber amplifier, wherein laser beams output by the seed laser adopt the optical fiber amplifier for energy amplification and then output laser, and the peak power of each pulse of the laser beams is more than 10 kilowatts.

3. The method for laser cutting a silicon wafer according to claim 2, characterized in that: the seed laser is a Q-switched fiber laser.

4. The method for laser cutting a silicon wafer according to claim 2, characterized in that: the seed laser is a gain-modulated semiconductor fiber coupled laser.

5. The method for laser cutting a silicon wafer according to claim 1, characterized in that: the output pulse width of the fiber laser is 1 ps-300 ps.

6. The method for laser cutting a silicon wafer according to claim 1, characterized in that: the output pulse width of the fiber laser is 0.5 ns-100 ns.